The present invention relates to a method and device for the optimization of the drawing process on autoleveller drawframes in the textile industry.
In the textile industry, the function of an autoleveller drawframe is to draw out slivers of textile fibers by a factor of four to eight and thus make them as uniform as possible. The most frequently occurring type of these autoleveller drawframes operates in short-staple spinning (e.g., in cotton spinning) on the principle of the closed control loop. Here the textile material is drawn out in a drafting zone in proportion to the peripheral speeds of two pairs of drafting rollers (equal to the amount of draft). In a measuring element at the end of the drafting zone, the cross-section of the sliver is measured and the value thus obtained is compared against a target value. The resultant error signal acts in known fashion upon the amount of draft through a correcting element.
In long-staple spinning, most autoleveller drawframes operate on the principle of the open control loop. In such a system, the sliver cross-section entering the drafting unit is measured by a measuring element and the draft is controlled accordingly. It is important here to take into account both the delay time T of the sliver between the measuring element and the correcting element and also the overall amplification V of the signal between the measuring element and the correcting element.
In a closed control loop, on the other hand, because of the so-called dead time between the drafting zone and the measuring element, it is not possible to equalize short-term variations in cross-section. To improve matters, i.e., to equalize short-term variations as well, it is possible to add a second measuring element located before the autoleveller drafting unit. This cooperates with the autoleveller drafting unit as an open control loop. Thus, a combination of an open and a closed control loop is achieved within the same autoleveller drafting unit.
Furthermore, it is known that in open control loops it is not very easy to accurately adjust the overall amplification V and the delay time T in the control elements for the open control loop. Theoretically, it should be possible to determine precisely the delay time T from the point of time of measurement to the action in the correcting element. This is not the case in practice, however. Furthermore, this delay time is also influenced by mass effects. Additional influences are exerted by special features occurring in the drafting of fibrous slivers. Appropriate information on this has been provided in the technical literature.
Similar circumstances apply also to the overall amplification V. It might be thought that the target draft in the drafting zone could be established theoretically from the measurement signal. However, for the same practical reasons this solution cannot be considered. In most cases, therefore, adjustment is made empirically by autolevelling the sliver, then checking on the testing apparatus and finding the optimum of the comparison by changing the parameters.